The invention relates to self-adhesive addition-crosslinking silicone compositions and addition-crosslinked silicone elastomers and composite materials prepared therefrom.
It is known that the adhesion of addition-crosslinked silicone elastomers to numerous substrates, such as plastics, metals and glasses, is poor, i.e. if an addition-crosslinking silicone elastomer material is applied to a substrate and then crosslinked, the silicone elastomer formed can, as a rule, be peeled away from the substrate surface without problems. Only small tensile forces; frequently, even spontaneous delamination of the silicone elastomer from the substrate is found. However, since strong and permanent adhesion of the silicone elastomer to the substrate is of primary importance in numerous applications, a large number of special measures have been proposed for achieving a strong bond between substrate and silicone elastomer.
In principle, the adhesive strength of the silicone elastomer/substrate composite can be increased by suitably changing the chemical and/or physical characteristics of the substrate or its surface prior to application of the addition-crosslinking silicone elastomer composition. This can be effected, for example, by pretreating the substrate surface with adhesion-promoting additives (so-called primers), by subjecting the substrate surface to a plasma treatment, by formulating the substrate to contain special additives, by selectively adjusting the morphology of the substrate, by increasing the surface roughness, etc. These measures have, inter alia, the disadvantage that additional process steps are required. As the characteristics of the substrate often have to meet special requirements, use of these methods of increasing adhesive strength is often not possible.
The adhesive strength of the silicone elastomer/substrate composite can also be increased by selectively changing the chemical and/or physical characteristics of the addition-crosslinking silicone elastomer material. Numerous adhesion-promoting additives are known which, when mixed with the uncrosslinked silicone material, give rise to self-adhesion of the resulting silicone elastomer to various substrates. These include compounds which contain highly reactive functional groups, such as alkoxy, epoxy, carboxyl, amino, etc., these groups generally being chosen so that the adhesion promoter is capable of reacting both with the substrate and with a silicone elastomer component. Although such adhesion promoters may make it possible to dispense with a pretreatment of the substrate, the adhesive strength achieved frequently does not meet the desired requirements. In addition, an increase in the adhesive strength by means of higher content of these adhesion promoters is limited, since the highly reactive groups contained exhibit increasingly disadvantageous effects on performance characteristics such as shelf-life, crosslinking characteristics (inhibition), toxicological safety, etc. For these reasons, interest focused on keeping the content of adhesion promoters as low as possible.
EP-A-686 671 describes a self-adhesive adhesion-crosslinking material which employs no special adhesion promoter, because the adhesion-promoting component is either an organohydrogenpolysiloxane which has on average at least two SiH groups per molecule and whose monovalent Si-bonded radicals comprise at least 12 mol % of hydrocarbon radicals having an aromatic ring; or is a compound which has on average at least one SiH group per molecule and contains a group consisting of two aromatic rings, the two aromatic rings being separated from one another by xe2x80x94R13R14Sixe2x80x94, xe2x80x94R13R14SiOxe2x80x94, xe2x80x94OR13R14SiOxe2x80x94 or xe2x80x94R13R14SiOR13R14Sixe2x80x94xe2x80x94, the radicals R13 and R14 being monovalent hydrocarbon radicals. The adhesion-promoting component can thus simultaneously function as the crosslinking agent of the silicone elastomer material. Good adhesion to organic plastics (especially ABS) is achieved with this composition, while at the same time the cured or partially cured products exhibit good demoldability from the metallic vulcanization mold (chromium- or nickel-coated steel mold or mold of an aluminum alloy). The high content of greater than 12 mol % of radicals containing aromatic rings in the SiH-containing, adhesion-promoting component results, however, in considerable incompatibility with the other components of the addition-crosslinking silicone elastomer material. This leads to partial separation (exudation) during storage, necessitating repeated homogenization of the ingredient containing this component before use. This incompatibility, which is already evident from a milky turbidity of the uncrosslinked material, also manifests itself in substantially reduced transparency of the silicone elastomer parts produced therefrom. If the adhesion-promoting component simultaneously acts as a crosslinking agent of the silicone elastomer composition, the incompatibility leads to vulcanization problems, which result in inhomogeneous network formation and poor mechanical vulcanization properties. To overcome these vulcanization problems, it is necessary, in addition to the adhesion-promoting SiH-containing component, to use an SiH-containing crosslinking agent completely compatible with the silicone elastomer material, which however results in other disadvantages, for example higher values of the compression set, and higher tendency to exudation of the adhesion-promoting component. The high content of greater than 12 mol % of radicals containing aromatic rings in the SiH-containing, adhesion-promoting component also results in a considerable structural viscosity and thixotropy of the silicone elastomer material, which is undesired in numerous applications, for example, injection molding of liquid silicone rubber. Finally, the adhesion of this composition to metals is also insufficient.
EP-A-875 536 describes a self-adhesive adhesion-crosslinking silicone rubber mixture which is distinguished by the fact that
a) the SiH crosslinking agent contains at least 20 SiH groups, other radicals being aliphatically saturated,
b) an alkoxysilane and/or alkoxysiloxane having epoxy functional groups is/are present, and
c) a peroxide is optionally present.
The use of glycidyloxypropyltrimethoxysilane (Glymo) is particularly preferred. The silicone rubber mixture described in EP-A-875 536 is particularly suitable for the production of composite shaped articles which consist of the silicone elastomer and an organic plastic. However, the composition described in EP-A-875 536 has the disadvantage that sufficient adhesive strength can be achieved only with the use of very SiH-rich crosslinking agents having on average at least 20 SiH groups per molecule. In the examples there, crosslinking agents having 30 SiH groups per molecule are used. The use of such polyfunctional crosslinking agents considerably reduces the shelf-life of addition-crosslinking silicone rubber mixtures, i.e. the flowability is considerably impaired, which may lead to stiffening of the material. As a result, proper processing of the material, for example by injection molding, is no longer possible. In addition, in order to achieve high adhesive strength, it is necessary to use relatively large amounts of alkoxysilane/alkoxysiloxane having epoxy functional groups, with the result that the crosslinking rate is considerably reduced. Although this can be partly compensated by using a peroxide, as described in EP-A-875 536, only peroxides having a low initiation temperature, such as the 2,4-dichlorobenzoyl peroxide described, are suitable for this purpose, due to the necessarily low crosslinking temperature (softening of the organic plastic). These peroxides on the one hand are toxicologically very unsafe owing to the cleavage products and secondary products liberated (PCB problem) and on the other hand further impair the shelf-life of the material.
In summary, it may be said that none of the conventional addition-crosslinking silicone elastomer compositions satisfactorily meet the requirements set for a self-adhesive silicone elastomer material which is to be used in particular for the production of composite shaped articles or for casting electric/electronic parts, namely:
a) good flowability and shelf-life,
b) high crosslinking rate at relatively low temperatures,
c) high adhesive strength on organic plastics, metals and glasses,
d) easy demoldability from vulcanization molds,
e) toxicological safety,
f) high level of performance characteristics, especially (transparency, noncorrosiveness, and good mechanical property profile.
It was therefore an object of the present invention to provide an addition-crosslinking silicone elastomer material which has good self-adhesion to organic plastics, metals and glasses, does not have the above disadvantages, and meets the desired requirements as previously discussed.
The invention relates to self-adhesive addition-crosslinking silicone compositions which comprise
(A) diorganopolysiloxane(s) of the general formula (1)
R1aR2bSiO(4xe2x88x922xe2x88x92b)/2xe2x80x83xe2x80x83(1)
xe2x80x83in which
R1 is a hydroxyl radical or a monovalent, optionally halogen-substituted hydrocarbon radical optionally containing O, N, S or P atoms, having 1 to 20 carbon atoms, and being free of aliphatically unsaturated groups,
R2 is a monovalent, aliphatically unsaturated, optionally halogen-substituted hydrocarbon radical optionally containing O, N, S or P atoms and having 2 to 10 carbon atoms,
b has a value from 0.003 to 2,
xe2x80x83with the proviso that 1.5 less than (a+b) less than 3.0, that on average at least two aliphatically unsaturated radicals R2 are present per molecule and that the viscosity of the diorganopolysiloxane(s) (A), determined at 25xc2x0 C., is 1 mPaxc2x7s to 40,000. Paxc2x7s,
(B) organohydrogenpolysiloxane(s) of the general formula (2)
R3cR4dR5eHfSiO(4xe2x88x92cxe2x88x92dxe2x88x922exe2x88x92f)/2xe2x80x83xe2x80x83(2)
xe2x80x83in which
R3 is a monovalent aliphatically saturated hydrocarbon radical having 1 to 20 carbon atoms,
R4 is (a) an optionally halogen-substituted monovalent hydrocarbon radical having 6 to 15 carbon atoms which contains at least one aromatic C6-ring, and/or (b) a halogen-substituted, saturated monovalent hydrocarbon radical optionally containing O, N, S or P atoms and having 2 to 20 carbon atoms,
R5 is a bivalent, optionally halogen-substituted hydrocarbon radical Si-bonded at both ends, optionally containing O, N, S or P atoms and having 6 to 20 carbon atoms, and c, d, e and f denote positive numbers, with the proviso that the organohydrogenpolysiloxane (B) contains on average 3 to less than 20 SiH groups per molecule, that the relationship: 0.05 less than 100 (d+e)/(c+d+e+f) less than 12 is fulfilled, and that the viscosity of the organohydrogenpolysiloxane (B), determined at 25xc2x0 C., is 1 mPaxc2x7s to 100 Paxc2x7s,
(C) organosilicon compounds having epoxy groups and hydrolyzable groups, of the general formula (3)
R7gR8hR9iSiO(4xe2x88x92gxe2x88x92hxe2x88x92i)/2xe2x80x83xe2x80x83(3)
xe2x80x83and/or their partial hydrolysis products, in which
R7 is a hydrogen radical, a hydroxyl radical or an optionally halogen- or cyano-substituted, saturated monovalent hydrocarbon radical optionally containing O, N, S or P atoms and having 1 to 20 carbon atoms,
R8 is an optionally halogen-substituted monovalent hydrocarbon radical containing at least one epoxy group, optionally containing O, N, S or P atoms and having 2 to 20 carbon atoms,
R9 is a hydrolyzable, monovalent optionally halogen-substituted hydrocarbon radical bonded to Si via an SiCxe2x80x94, Sixe2x80x94Oxe2x80x94Nxe2x80x94or Sixe2x80x94Nxe2x80x94 link, optionally containing O, N, S or P atoms and having 1 to 20 carbon atoms,
xe2x80x83with the proviso that 4 greater than gxe2x89xa70, 4 greater than h greater than 0, 4 greater than i greater than 0, 4xe2x89xa7(h+i) greater than 0 and 4xe2x89xa7(g+h+i), and
(D) a hydrosilylation catalyst.
Organohydrogenpolysiloxane (B) acts as an adhesion promoter and simultaneously as a crosslinking agent.
The advantageous properties of the silicone compositions derive from in the fact that the self-adhesion is achieved by a component present in every addition-crosslinking material, namely the SiH-containing crosslinking agent (B), in combination with the organosilicon compound (C) having epoxy-functional and hydrolyzable radicals, it merely being necessary for the SiH crosslinking agent (B) to contain a few groups which reduce the compatibility with the other components of the material (especially with the diorganopolysiloxane). These groups are not reactive functional groups, but are preferably phenyl groups, with the result that the toxicological safety of the material (e.g. drinking water approval; BGA/FDA approval) is preserved, no vulcanization problems occur, the shelf-life is sufficient, the transparency of the crosslinked silicone elastomer is maintained, and no components which exude or are extractable are added. The combination of the SiH crosslinking agent (B) having reduced compatibility, with an organosilicon compound (C) having epoxy-functional and hydrolyzable radicals, makes it possible, first, to keep the content of incompatible groups in the SiH crosslinking agent low, and secondly, to achieve the adhesion-promoting activity of the organosilicon compound (C) having epoxy-functional and hydrolyzable radicals even in the case of relatively low SiH functionality of the SiH crosslinking agent. Only the combination of the two components (B) and (C) leads to synergistic self-adhesion effects of these two components.
In particular, the present composition is distinguished by the fact that
a) the crosslinking rate is scarcely reduced,
b) the transparency of the crosslinked silicone elastomers is not impaired,
c) there is no need to accept any disadvantageous changes in the mechanical elastomer properties,
d) the adhesion-promoting component (B) simultaneously acts as a crosslinking agent (no additional SiH crosslinking agent required),
e) strong self-adhesion can be achieved even on metals without hindering the demoldability from metal vulcanization molds (it was found that the adhesion to metal shortly after crosslinking permits demolding of the silicone elastomer part; if, however, the silicone elastomer/metal composite is stored, the silicone elastomer grows strongly and permanently onto the metal surface within a short time),
f) the flowability of the uncrosslinked material is scarcely impaired.
Although the adhesion-promoting component (B) of the present invention also has reduced compatibility with the other components of the material, which is evident from turbidity on mixing in, this turbidity disappears completely as soon as the material is heated for the purpose of crosslinking; this indicates a homogeneous distribution of the molecules of the crosslinking agent in the material at the time of crosslinking. If, on the other hand, the adhesion-promoting SiH-containing component (B) contains phenyl groups 12 mol % or more of the radicals, turbidity also persists at customary crosslinking temperatures and indicates inhomogeneous network formation, which can also be demonstrated on the basis of the optical properties, crosslinking characteristics, and on the basis of the mechanical properties.
The components (A), (B) and (C) may each constitute a single compound or a mixture of different compounds.
Examples of the radicals R1 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl, and octadecyl radicals; cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl and bornyl radicals; aryl or aralkyl radicals such as the phenyl, ethylphenyl, tolyl, xylyl, mesityl, and naphthyl radicals; aralkyl radicals such as the benzyl, 2-phenylpropyl and phenylethyl radicals; and those derivatives of the above radicals which are halogenated and functionalized with organic groups, such as the 3,3,3-trifluoropropyl, 3-iodopropyl, 3-isocyanatopropyl, aminopropyl, methacryloyloxyrmethyl, and cyanoethyl radicals. Preferred radicals R1 contain 1 to 10 carbon atoms and optionally contain halogen substituents. Particularly preferred radicals R1 are the methyl, phenyl and 3,3,3-trifluoropropyl radicals, in particular the methyl radical.
The radicals R2 are obtainable by a hydrosilylation reaction. Examples of these are alkenyl and alkynyl radicals such as the vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radicals; cycloalkenyl radicals such as the cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl norbornenyl, 4-cyclooctenyl, and cyclooctadienyl radicals; aralkenyl radicals such as the styryl and styrylethyl radicals; and those derivatives of the above radicals which are halogenated and/or contain heteroatoms, such as the 2-bromovinyl, 3-bromo-1-propynyl, 1-chloro-2-methylallyl, 2-(chloromethyl)allyl, styryloxy, allyloxypropyl, 1-methoxyvinyl, cyclopentenyloxy, 3-cyclohexenyloxy, acryloyl, acryloyloxy, methacryloyl, and methacryloyloxy radicals. Preferred radicals R2 are the vinyl, allyl and 5-hexenyl radicals, in particular the vinyl radical.
In the case of the diorganopolysiloxanes (A) of the general formula (1), the viscosity determined at 25xc2x0 C. is preferably 100 mPaxc2x7s to 30,000 Paxc2x7s. More preferably, the viscosity range is from 1 to 30,000 Paxc2x7s. Depending on the type of addition-crosslinking material, different viscosity ranges may be preferred. Viscosities from 100 to 10,000 mPaxc2x7s are particularly preferred for the materials known as RTV-2 (room temperature vulcanizing) compositions, from 1 to 100 Paxc2x7s for LSR (liquid silicone rubber) compositions, and from 2000 to 40,000 Paxc2x7s for HTV (high temperature vulcanizing) compositions.
Examples of R3 are alkyl radicals such as the methyl, ethyl, propyl, isopropyl, tert-butyl, n-octyl, 2-ethylhexyl and octadecyl radicals; and cycloalkyl radicals such as the cyclopentyl, cyclohexyl, norbornyl, and bornyl radicals. Preferred radicals R3 are hydrocarbon radicals having 1 to 10 carbon atoms. A particularly preferred radical R3 is the methyl radical.
Examples of R4 (a) are the phenyl, tolyl, xylyl, biphenylyl, anthryl, indenyl, phenanthryl, naphthyl, benzyl, phenylethyl and phenylpropyl radicals, and those derivatives of the above radicals which are halogenated and functionalized with organic groups, such as the o-, m- or p-chlorophenyl, pentafluorophenyl, bromotolyl, trifluorotolyl, phenoxy, benzyloxy, benzyloxyethyl, benzoyl, benzol-oxy, p-tert-butylphenoxypropyl, 4-nitrophenyl, quinolinyl, and pentafluorobenzoyloxy radicals.
Examples of hydrocarbon radicals R4 (b) having 2 to 20 carbon atoms are the 3-chloropropyl, 3-bromopropyl, 3,3,3-trifluoropropyl, 2-fluoroethyl, 1,1-dihydroperfluorododecyl, and 2-cyanoethyl radicals. Particularly preferred radicals R4 are the phenyl radical and the 3,3,3-trifluoropropyl radical.
Preferred radicals R5 correspond to the general formula (4)
xe2x80x94(O)sxe2x80x94(R6)txe2x80x94(O)uxe2x80x94(X)wxe2x80x94(O)uxe2x80x94(R6)txe2x80x94(O)sxe2x80x94xe2x80x83xe2x80x83(4)
in which
s, t, u and w, independently of one another, denote the values 0, 1 or 2,
R6 may be identical or different and denotes a bivalent, optionally halogen-substituted hydrocarbon radical which optionally contains O, N, S or P atoms, is free of aliphatically unsaturated aliphatic groups and contains 1 to 10 carbon atoms, such as xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CH2xe2x80x94CH2xe2x80x94CH2xe2x80x94, xe2x80x94CF2xe2x80x94, xe2x80x94CH2xe2x80x94CF2xe2x80x94, xe2x80x94CH2xe2x80x94CH(CH3)xe2x80x94, xe2x80x94C(CH3)2xe2x80x94, xe2x80x94CH2xe2x80x94C(CH3)2xe2x80x94, xe2x80x94C(CH3)2xe2x80x94CH2xe2x80x94, CH2xe2x80x94CH2xe2x80x94Oxe2x80x94 or xe2x80x94CF2xe2x80x94CF2xe2x80x94Oxe2x80x94,
xe2x80x94(X)xe2x80x94 denotes a bivalent radical which may be xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94Oxe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94Sxe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94SO2xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94C(CH3)2xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94C(CF3)2xe2x80x94Phxe2x80x94, xe2x80x94Phxe2x80x94C(O)xe2x80x94Phxe2x80x94, cyclohexylene or norbornylene, xe2x80x94Phxe2x80x94 designating a phenylene group. A particularly preferred radical R5 is the phenylene radical.
The organohydrogenpolysiloxane (B) preferably contains 5 to 18 SiH groups per molecule. The viscosity of the component (B), measured at 25xc2x0 C., is preferably 2 mPaxc2x7s to 1 Paxc2x7s. Owing to the labile nature of the SiH group, the component (B) may have a low content, typically  less than 100 ppm by weight, of Si-bonded OH groups, due to the method of preparation.
Examples of hydrocarbon radicals R7 are alkyl radicals such as the methyl, ethyl, n-propyl, isopropyl, tert-butyl, n-pentyl, isopentyl, neopentyl, tert-pentyl, n-octyl, 2-ethylhexyl, 2,2,4-trimethylpentyl, n-nonyl and octadecyl radicals; cycloalkyl radicals such as the cyclopentyl, cyclohexyl, cycloheptyl, norbornyl, adamantylethyl, and bornyl radicals; aryl radicals such as the phenyl, ethylphenyl, tolyl, xylyl, mesityl, and naphthyl radicals; aralkyl radicals such as the benzyl, phenylethyl, and phenylpropyl radicals; alkenyl or alkynyl radicals such as the vinyl, allyl, isopropenyl, 3-butenyl, 2,4-pentadienyl, butadienyl, 5-hexenyl, undecenyl, ethynyl, propynyl and hexynyl radicals; cycloalkenyl radicals such as the cyclopentenyl, cyclohexenyl, 3-cyclohexenylethyl, 5-bicycloheptenyl, norbornenyl, 4-cyclooctenyl, and cyclooctadienyl radicals; aralkenyl radicals such as the phenylethenyl and phenylethynyl radical; and those derivatives of the above radicals which are halogen-substituted or contain heteroatoms, such as the 3-chloropropyl, 3-bromopropyl, decafluoro-1,1,2,2-tetrahydrooctyl, (p-chloromethyl)phenyl, (p-chloromethyl)phenethyl, hydroxymethyl, hydroxyethyl, hydroxypropyl, hydroxybutyl, 2-bromovinyl, 2-allyloxymethyl, acetyl, acetoxymethyl, acetoxyethyl, acetoxypropyl, 3-phenoxypropyl, benzoyloxypropyl, mercaptopropyl, cyanoethyl, cyanopropyl, 3-cyanobutyl, 3-isocyanatopropyl, 2-(carbomethoxy)ethyl, 10-(carbomethoxy)decyl, 2-(carboxymethylthio)ethyl, 3-carboxypropyl, aminomethyl, aminoethyl, aminopropyl, aminohexyl, aminoethylaminopropyl, 3-N-allylamino)propyl, (aminoethylaminomethyl)phenethyl, m-aminophenyl, 3-(m-aminophenoxy)propyl, 3-acryloyloxypropyl, 3-acryloyloxy-2-hydroxypropyl,4-(acryloyloxymethyl)phenethyl, methacryloyloxymethyl, methacryloyloxyethyl, and methacryloyloxypropyl radicals. Preferred radicals R7 are the methyl, ethyl, propyl, butyl, octyl, vinyl, allyl, phenyl, 3,3,3-trifluoropropyl and cyanopropyl radicals. Particularly preferred radicals R7 are the methyl, vinyl and phenyl radicals.
Examples of the radicals R8 are the epoxyethyl, 2,3-epoxypropyl, 3,4-epoxybutyl, 5,6-epoxyhexyl, 9,10-epoxydecyl, glycidyloxy, 3-glycidyloxypropyl, glycidyloxyisobutyl, 2-methylglycidyloxypropyl, 3-phenylglycidyloxypropyl, glycidyloxyphenylnonyl, glycidyloxybenzylethyl, 3,4-epoxycyclohexyl, 2-(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 1,4-epoxycyclohexyl, and 2-(1,4-epoxycyclohexyl)ethyl radicals. Preferred radicals R8 are the 3,4-epoxycyclohexyl, 3-(3,4-epoxycyclohexyl)propyl and glycidyloxypropyl radicals. R8 preferably has 2 to 10 carbon atoms. A particularly preferred radical R8 is the glycidyloxypropyl radical.
R9 denotes a hydrolyzable, monovalent, optionally halogen-substituted hydrocarbon radical bonded to Si via an Sixe2x80x94Oxe2x80x94Cxe2x80x94, Sixe2x80x94Oxe2x80x94Nxe2x80x94 or Sixe2x80x94N-link, optionally containing O, N, S or P atoms and having 1 to 20 carbon atoms.
Examples of the radicals R9 are
a) alkoxy, alkenoxy or aryloxy groups of the general formula xe2x80x94OR10, such as the methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, tert-butoxy, 2-ethylbutoxy, 2-ethylhexyloxy, vinyloxy, allyloxy, isopropenyloxy, cyclobutenyloxy, cyclohexenyloxy, 1,3-butadienyloxy, propargyloxy, phenoxy, benzyloxy, and m- and p-vinylbenzyloxy radicals;
b) acyloxy groups of the general formula xe2x80x94OCOR10, such as the formyloxy, acetoxy, 2-ethylhexanoyloxy, acryloyloxy, methacryloyloxy, benzoyloxy, and norbornyl-acetoxy radicals;
c) amino groups of the general formula xe2x80x94NH2, xe2x80x94NHR10, and xe2x80x94NHR102, such as the dimethylamino, diisopropylamino, allylamino, n-butylamino, sec-butylamino, and cyclohexylamino radical;
d) oxime groups of the general formula xe2x80x94ONxe2x95x90CH2, xe2x80x94ONxe2x95x90CHR10, and xe2x80x94ONxe2x95x90CR102, such as the methyl ethyl ketoxime, methyl isobutyl ketoxime, methyl n-amyl ketoxime, and dimethyl ketoxime radicals;
e) amido groups of the general formula xe2x80x94NHxe2x80x94C(xe2x95x90O)xe2x80x94R10 or xe2x80x94NR10xe2x80x94C(xe2x95x90O)xe2x80x94R10, such as the N-methylbenzamido and N-methylacetamido radicals;
f) aminoxy groups of the general formula xe2x80x94ONH2, xe2x80x94ONHR10 or xe2x80x94ONR10z, such as the hydroxylamino radical; and
g) those derivatives of the abovementioned radicals which are halogen-substituted or contain heteroatoms or have an otherwise complex composition, such as p-aminophenoxy, 2-methoxyethoxy, 1-methoxy-2-propoxy, 1-methoxy-isopropenyloxy, methoxyethoxyethoxy, 1-methoxy-2-methylpropenyloxy, acryloyloxymethoxy, methacryloyloxy(polyethyleneoxy), furyloxy, and N-vinyl-formamido radicals, and xe2x80x94Oxe2x80x94Phxe2x80x94C(xe2x95x90O)xe2x80x94Ph, xe2x80x94Oxe2x80x94C(CF3)xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94CF3, xe2x80x94Oxe2x80x94C(CH3)xe2x95x90CHxe2x80x94C(xe2x95x90O)xe2x80x94CH3, xe2x80x94Oxe2x80x94C(CH3)2xe2x80x94CHxe2x95x90CH2, xe2x80x94NHxe2x80x94C(xe2x95x90O)xe2x80x94CH3, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CH2Br, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94CF3, xe2x80x94Oxe2x80x94C(xe2x95x90O)xe2x80x94Cxe2x89xa1xe2x80x94CH or xe2x80x94Oxe2x80x94CH2xe2x80x94C(xe2x95x90O)xe2x80x94Oxe2x80x94Si(CH3)3,
where the radicals R10 represent monovalent aliphatic or aromatic, saturated or unsaturated, optionally halogen-substituted hydrocarbon radicals having 1 to 10 carbon atoms. Preferred radicals R9 are the alkoxy radicals such as the methoxy, ethoxy, propoxy, and butoxy radicals. The particularly preferred radical R9 is the methoxy radical. A particularly suitable organosilicon compound (C) is glycidyloxypropyltrimnethoxysilane (Glymo).
The radicals R1 to R10 in all above formulae may be identical or different. Preferred heteroatoms are N, O and S. Preferred halogen substituents are F, Cl and Br.
Preferably 0.1 to 50 parts by weight, in particular 0.5 to 10 parts by weight, of organohydrogenpolysiloxane (B) and 0.1 to 10 parts by weight, in particular 0.5 to 5 parts by weight, of organosilicon compound (C) are used per 100 parts by weight of diorganopolysiloxane (A).
Hydrosilylation catalyst (D) serves as a catalyst for the hydrosilylation addition reaction between the aliphatically unsaturated hydrocarbon radicals R2 of the diorganopolysiloxanes (A) and the silicon-bonded hydrogen atoms of the organohydrogenpolysiloxanes (B). Numerous suitable hydrosilylation catalysts are described in the literature. In principle, all hydrosilylation catalysts corresponding to the prior art and used in addition-crosslinking silicone rubber materials can be used.
Metals and their compounds, such as platinum, rhodium, palladium, ruthenium and iridium, preferably platinum, can be used as hydrosilylation catalysts (D). The metals can optionally be fixed on finely divided support materials, such as active carbon, metal oxides, such as alumina, or silica.
Platinum and platinum compounds are preferably used. Particularly preferred platinum compounds are those which are soluble in polyorganosiloxanes. The soluble platinum compounds used may be, for example, the platinum-olefin complexes of the formulae (PtCl2.olefin)2 and H(PtCl3.olefin), alkenes having 2 to 8 carbon atoms such as ethylene, propylene, isomers of butene and of octene, and cycloalkenes having 5 to7 carbon atoms such as cyclopentene, cyclohexene and cycloheptene preferably being used. Further soluble platinum catalysts are the platinum-cyclopropane complexes of the formula (PtCl2C3H6)2, the reaction products of hexachloroplatinic acid with alcohols, ethers and aldehydes and mixtures thereof or the reaction product of hexachloroplatinic acid with methylvinylcyclotetrasiloxane in the presence of sodium bicarbonate in ethanolic solution. Platinum catalysts with phosphorous, sulfur and amine ligands may also be used, e.g. (Ph3P)2PtCl2. Complexes of platinum with vinylsiloxanes, such as symdivinyltetramethyldisiloxane, are particularly preferred.
The amount of hydrosilylation catalyst (D) used depends on the desired crosslinking rate and economic points of view. Preferably, 1xc3x9710xe2x88x925 to 5xc3x9710xe2x88x922 part by weight, in particular 1xc3x9710xe2x88x923 to 1xc3x9710xe2x88x922 part by weight of platinum catalysts, calculated as platinum metal, is used per 100 parts by weight of diorganopolysiloxanes (A).
The self-adhesive addition-crosslinking silicone compositions can optionally contain conventional further components (E), such as fillers, inhibitors, stabilizers, pigments and catalysts.
In order to achieve a sufficiently high mechanical strength of the crosslinked silicone rubber, it is preferable to incorporate actively reinforcing fillers as component (F) into the addition-crosslinking silicone compositions. The actively reinforcing fillers (F) preferably used are, in particular, precipitated and pyrogenic silicas, and mixtures thereof. The specific surface area of these actively reinforcing fillers should be at least 50 m2/g or preferably in the range from 100 to 400 m2/g according to the determination by the BET method. Such actively reinforcing fillers are very well known materials in the area of silicone rubbers.
The compounding of the self-adhesive addition-crosslinking silicone compositions is effected by mixing the abovementioned ingredients in any desired sequence. The crosslinking of the self-adhesive addition-crosslinking silicone compositions is preferably effected by heating, preferably at 30xc2x0 C. to 250xc2x0 C., preferably at at least 50xc2x0 C., in particular at at least 100xc2x0 C., and preferably at not more than 200xc2x0 C., more preferably at not more than 180xc2x0 C.
The invention also relates to the addition-crosslinked silicone elastomers prepared from the crosslinkable compositions.
The silicone compositions can be bonded to a substrate by applying the silicone compositions to the substrate and then crosslinking them, preferably by heating to 30 to 250xc2x0 C., to give a composite material. The self-adhesive addition-crosslinking silicone composition can advantageously be used in particular where good adhesive strength between the addition-crosslinked silicone elastomer and a substrate, preferably an organic polymer, metal or glass substrate, is desired. The substrate may be present as a shaped article, film or coating. The self-adhesive addition-crosslinking silicone compositions are suitable for the production of composite materials by coating, adhesive bonding or casting, and for the production of shaped articles.
The self-adhesive addition-crosslinking silicone compositions are particularly suitable for casting and for adhesively bonding electrical and electronic parts and for the production of composite shaped articles. Composite shaped articles are understood here as meaning a uniform shaped article comprising a composite material which is composed of a silicone elastomer part produced from the silicone compositions and at least one substrate, so that there is a strong, permanent bond between the two parts. Such a composite shaped article is preferably produced by processing an organic polymer or polymer precursor to give a shaped article, followed by bringing the silicone composition into contact with this shaped article and crosslinking. This can be effected, for example, by injection molding, by means of extrusion, and by the so-called press-molding method. Composite materials and in particular composite shaped articles can be used in a very wide range of applications, for example in the electronics, household appliance, consumables, construction, and automotive industries, in medical technology, in the production of sport and leisure articles, etc.
In the following examples, unless stated otherwise in each case, all pressures are 0.10 MPa (abs.), and all temperatures are 20xc2x0 C.